This invention relates to gas turbine, or jet, engines, and, in particular, to engines which include afterburners downstream of a core engine with means for adding fuel to exhaust flow for augmenting thrust.
A bypass jet engine includes a low pressure compressor (LPC) for pressurizing inlet air to the engine; a core engine for producing thrust and also for driving the LPC; and, further, may include an afterburner in which fuel is added to the core engine exhaust, which is then ignited to provide thrust augmentation. The bypass engine is so called because it includes an annular outer casing which is substantially concentrically mounted about the core engine casing to form an annular bypass duct therebetween. The discharge air from the LPC is divided between the bypass duct and the core engine.
In general, engine lines mature and as uprated versions of existing engines are derived, one of the design methods to obtain increased engine output has been to increase turbine inlet temperature with a consequent increase in the inlet temperature to the afterburner. The flashback margin of the fuel/air mixture scrubbing the afterburner hardware is thereby proportionately reduced. Flashback is the movement of the flame front upstream of its design position against the direction of the main gas flow and toward the flameholder and the fuel injection source. Flashback margin is the difference in actual temperature of the exhaust gases and the temperature thereof which would cause flashback.
If the turbine exhaust temperatures increase sufficiently, then the afterburner flame front would move upstream in the afterburner combustion chamber toward the flameholder. The flameholder would then increase in temperature due to the radiation/convective heat loads, which could result in reduced flameholder design life.
Accordingly, it is an object of the present invention to provide an improved flameholder.
Another object of the invention is to provide means for cooling the flameholder.
Another object of the invention is to provide means for increasing flashback margin in an afterburner.